Nadene,
Journey North http://www.learner.org/jnorth/
is a great way to get kids involved in the changing seasons -
lots of great teacher resources -
Bucket Buddies  http://www.ciese.org/curriculum/bucketproj/
is great if you don't mind bringing pond water into your classroom
- perhaps both of these are best for the older end of your
spectrum
(I would love to see the things you collect when you're done!)
Best wishes,

Clare Caddell
K-4 Technology
Hermon Elementary School
Hermon, ME  04401